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The purpose of a bridge navigational watch alarm system is to monitor bridge activity and detect operator disability which could lead to marine accidents.
The system monitors awareness of the Officer of the Watch (OOW) and automatically alerts the Master or another qualified person if, for any reason, the OOW becomes incapable of performing OOW duties.
This purpose is achieved by series of indications and alarm to alert first the OOW and, if he is not responding, then to alert Master or another qualified person.


                                                        IMO REQUIREMENTS
The BNWAS should incorporate the following operational modes:
- Automatic (Automatically brought into operation whenever the ship.s heading
or track control system is activated and inhibited when this system is not activated)
- Manual ON (In operation constantly)
- Manual OFF (Does not operate under any circumstances)

Once operational, the alarm system should remain dormant for a period of between 3 and 12 min (Td).
At the end of this dormant period, the alarm system should initiate a visual indication on the bridge.
If not reset, the BNWAS should additionally sound a first stage audible alarm on the bridge 15 s after the visual indication is initiated.
If not reset, the BNWAS should additionally sound a second stage remote audible alarm in the back-up officer’s and/or Master’s location 15 s after the first stage audible alarm is initiated.
If not reset, the BNWAS should additionally sound a third stage remote audible alarm at the locations of further crew members capable of taking corrective actions 90 s after the second stage remote audible alarm is initiated.

In vessels other than passenger vessels, the second or third stage remote audible alarms may sound in all the above locations at the same time. If the second stage audible alarm is sounded in this way, the third stage alarm may be omitted.
In larger vessels, the delay between the second and third stage alarms may be set to a longer value on installation, up to a maximum of 3 min, to allow sufficient time for the back-up officer and/or Master to reach the bridge.

Means may be provided on the bridge to immediately activate the second, and
subsequently third, stage remote audible alarms by means of an .Emergency Call. push button or similar.

It should not be possible to initiate the reset function or cancel any audible alarm from any device, equipment or system not physically located in areas of the bridge providing proper look out.
The reset function should, by a single operator action, cancel the visual indication and all audible alarms and initiate a further dormant period. If the reset function is activated before the end of the dormant period, the period should be re-initiated to run for its full duration from the time of the reset.
To initiate the reset function, an input representing a single operator action by the OOW is required. This input may be generated by reset devices forming an integralpart of the BNWAS or by external inputs from other equipment capable of registering physical activity and mental alertness of the OOW.
A continuous activation of any reset device should not prolong the dormant period or cause a suppression of the sequence of indications and alarms.

The alarm system should be capable of achieving the timings stated in section containing dormant period and alarm durations with an accuracy of 5% or 5 s, whichever is less, under all environmental conditions.
The means of selecting the Operational Mode and the duration of the Dormant Period (Td) should be security protected so that access to these controls should be restricted to the Master only.
If a malfunction of, or power supply failure to the BNWAS is detected, this should be
indicated. Means shall be provided to allow the repeat of this indication on a central alarm panel if fitted.

1 Operational controls
1.1 A protected means of selecting the operational mode of the BNWAS.
1.2 A protected means of selecting the duration of the dormant period of the BNWAS.
1.3 A means of activating the Emergency Call function if this facility is incorporated within the BNWAS.
1.4 Reset facilities

Means of activating the reset function should only be available in positions on the bridge giving proper look out and preferably adjacent to visual indications. Means of activating the reset function should be easily accessible from the conning position, the workstation for navigating and manoeuvring, the workstation for monitoring and the bridge wings.
2 Presentation of information
2.1 Operational mode
The operational mode of the equipment should be indicated to the OOW.
2.2 Visual indications
The visual indication initiated at the end of the dormant period should take the form of a flashing indication. Flashing indications should be visible from all operational positions on the bridge where the OOW may reasonably be expected to be stationed. The colour of the indication(s) should be chosen so as not to impair night vision and dimming facilities (although not to extinction) should be incorporated.

2.3 First stage bridge audible alarm
The first stage audible alarm which sounds on the bridge at the end of the visual indication period should have its own characteristic tone or modulation intended to alert, but not to startle, the OOW. This alarm should be audible from all operational positions on the bridge where the OOW may reasonably be expected to be stationed. This function may be engineered using one or more sounding devices. Tone/modulation characteristics and volume level should be selectable during commissioning of the system.
2.4 Second and third stage remote audible alarm
he remote audible alarm which sounds in the locations of the Master, officers and further crew members capable of taking corrective action at the end of the bridge audible alarm period should be easily identifiable by its sound and should indicate urgency. The volume of this alarm should be sufficient for it to be heard throughout the locations above and to wake sleeping persons.2
1 General
The equipment should comply with IMO resolutions A.694 (17), A.813 (19), their
associated international standards3 and MSC/Circ.982 regarding Guidelines for Ergonomic Criteria for Bridge Equipment and Layout.

2 Specific requirements
2.1 System physical integrity: All items of equipment forming part of the BNWAS should be tamper-proof so that no member of the crew may interfere with the system’s operation.
2.2 Reset devices: Reset devices should be designed and installed so as to minimise the possibility of their operation by any means other than activation by the OOW. Reset devices should all be of a uniform design and should be illuminated for identification at night.
2.3 Alternative reset arrangements may be incorporated to initiate the reset function from other equipment on the bridge capable of registering operator actions in positions giving proper look out.
3 Power supply
The BNWAS should be powered from the ship’s main power supply. The malfunction
indication, and all elements of the Emergency Call facility, if incorporated, should be powered from a battery maintained supply.

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